World's number one Serena Williams, 35, has forced her to pull out of this week's BNP Paribas Open at Indian Wells accusing a knee injury, the same joint that was said to hamper her at last year's US Open, where she fell in the semifinals against Karolina Pliskova. The withdrawal took even tennis insiders by surprise.

She decided also to miss the Miami Open later this month even if she is more or less a hometown favorite. "I have not been able to train due to my knees," she said. Her withdrawal means Germany's Angelique Kerber is set to replace her as world number one. Williams only returned to the Californian tournament in 2015 after a 14-year boycott following claims she had suffered racist abuse at the venue. Last year, Serena looked strong through the tournament but has not won, losing the final to Victoria Azarenka (6-4, 6-4). Serena, who resides in Palm Beach Gardens, Florida, has won Miami eight times. She has 23 Grand Slam singles titles and is probably the greatest singles player of all time. Now, she promised to return.